Electric furnace



ELECTRIC FURNACE Filed May 26, '1922/4 2 Sheets-Sheei l N6] y D HUBERT L .Foam/ELL April 20 1926. 1,581,872

R. L.. ROCKWELL y ELECTRIC FURNACE Filed May 26. 1.924 2 Sheets-Sheet 2 'Munn /5 Z0 INVENTOR ROBERT 23. Ho KM/ELL G energy derived Patented Apr. 20, 1926.

UNITED STATES PATENT ortica.

ROBERT L. ROCKWELL, 0F SEATTLE, WASHINGTON, .ASSIGNOR OF ONE-HALF TO F. B. FALLER, OF EVERETT, WASHINGTON.

ELECTRIC FURNACE.

Application filed May 26, 1924. Serial No, 715,854.

To all 'whom t may concern:

Be it known that I, ROBERT L. RooiwELL, a citizen of the United States, and a resident of Seattle, King County, Washington, have invented certain new and useful Improvements in Electric Furnaces, of which the following is a specification.

My invention relates to improvements in electric furnaces of the single phase t pe and methods of operating the same,an is particularly applicable to such furnaces using comparatively small currents at the higher arc voltages. y Y

It has been customary heretofore to operate single phase electric furnaces on single phase feeders tapped from polyphase supply systems. This practice is objectionable because of the unbalancing effect of such loads, especially where the furnace load is a considerable percentage of the output capacity of the source of supply. For this reason it is desirable to derive the single phase current jointly from the several phases of the polyphase system. In the past, however, this has Yrequired considerable additional equipment of a special nature, the use of which is both expensive and objectionable.

The smaller sizes of single hase furnaces of the arc type usually require the use of auxiliary reactors in either the primary or secondary circuits of the furnace transformers in order to stabilize the furnace arcs and reduce the severe fluctuations in load incident to their operation, even when the furnace transformers are specially constructed with built-iii7 reactance. For this reason where a poly hase electric furnace is supplied by a ban i of two transformers or their equivalent and it is desired to operate a small single phase furnace when the polyphase furnace is not in use, one of the transformers, an auxiliary reactor and suitable switches have reviously been used to that end. llt is evi( ent that the auxiliary reactor is an additional item of expense and is used only when the small furnace is in operation.

The object of my invention to provide improved means v: 4ic furnaces may be supplie; electric u a several curi-ent phases of' pol; li

systems.

iurtini operating single phase electric furnaces without the usual auxiliary reactors by using the impedances of a plurality of transformers in combination with the several phases of a polyphase source to stabilize the arc.

In the accompanying drawings I have illustrated diagrammatically several einbodiments of the invention.

Figure 1 is a diagrammatic illustration of one form of the invention for use in connection with two phase supply leads from a polyphase source, and Figure 2 is a simplilied diagram of the electrical connections showing the phase relation.

Figure 3 is a similar illustration of another form of the invention for use inw connection with three phase supply leads from a polyphase source.

Figure 4 isa vector diagram showing the secondary circuit voltage and current relations; the inductive reactance of the transformers and supply leads being neglected.'

Figure 5 is a iagram of connections of an adaptation of the invention for the operation of a single phase furnace in conjunction with a larger two phase furnace.

Like reference numerals are used to indicate like parts throughout the drawin Referring particularly to the form o theA invention illustrated in Figure 1, a single lphase electric furnace of the varc type 1 aving an upper movable electrode 2 and a lower fixed electrode 3 is shown in series circuit combination with the secondary windings 4 and 5, of a pair of transformers 6 and 7, respectively, by means of suitable connection conductors 8, 9 and 10.

A quadrature time phase relation between the two electromotive forces 11 and 12 induced in secondary windingsl and 5, as indicated in Figures 2 and 4, is obtained by connecting primary winding 13 of transformer 6 to one phase 124-14.- and primary winding u15 of transformer 7 to the second phase 16-16 of suitable two phase supply leads or bus bars.

atn

Since the transformer secondaries a and i 4which I have set the details shown and described in these specifications, as the invention may be-'embodied in various other forms. 'For example, there are a number of equivalent transformer combinations that may be substituted for the two transformers I prefer to use as illustrated in the accompanying diagrams. One of these is the lsubstitution of a polyphase transformer for the two single phase transformers. Another is the use of socalled auto-transformers -wherein the primary and secondary windings are not electi ically independent, as shown, for the transformers in my diagrams. It will be understood also that the single phase electric furnace is illustratedV ionlyvliagrammatically and that any type of single phase electric furnace may be used.-V Forinstance, instead of one-movable upper electrode and a single fixed lower electrode, as in my diagrams, the furnace may have two movable upper electrodes which may provide either one or two arcs, depending on the type. of furnace used.

Various other changes may be made from what I have disclosed herein without departing from the s irit ofv the invention orth in the appended claims as new and desire to secure by Letters-Patent of the United States.

Having thus described my invention, what Iclaim is:` f

l. The combination of an electric furnace, a plurality vof transformers'- energized by polyphase alternating' current and having substantially ar quadrature time phase relation between their respective secondary electromotive forces, and means for connecting the secondaries of 'said transformers in series circuit combination with the electrodes of said furnace.

2. The.combination of polyphase alternating current supply leads, means for using the several phasesof the saine to provide a quadrature time phase relation between two electromotivc forces, means of connecting the sources of said electromotive forces in series circuit combination with the electrodes of an electric furnace whereby said electromotive forces combine to form a resultant ymaries of said transformers toproduce av electrical pressure that is effective in forcing single hase current through said furnace.

' 3. T e combination of a single phase, electric furnace, a `plurality of transformers, polyphase alternating current supply leads, means of connecting the same to the prinominai quadrature phase relation between their respective secondary voltages and means for connecting the secondaries of said transformers in series with each other and` to the electrodes of saidffurnace.

4. The combination with a. single phase electric furnace, of two transformers whose secondaries are connected in series to the 4electrodes of said furnace and whose priwith a plurality of transformers with built.

in reactance, polyphase alternating current supply leads, means 'of so connecting the same to the primaries of said transformers as to provide a nominal two-phase relation between their secondary voltages, means of L connecting the secondaries of said transfarmers, and means of connecting the ends of said L to the electrodes ofsaid furnace,

vvwhereby the same may be supplied with single phase alternating current.

7. An electric arc furnace having a single movable upper electrode and a single fixed lower electrode, in combination with two transformers with built-in reactance, pol phase alternating current supply lea s, meansv of connecting said supply leads tothe primaries of said transformers to provide substantially a two-phase relation between their secondary voltages, means of L connecting the secondaries of said transformers and means of connecting the remaining terminals of said secondaries to the upper and lower electrodes respectively of said furnace.

8.l In combination, a single phase .electric furnace, a plurality of transformers, pol phase alternating current supply lea s, means Aof connecting the same to the pri:

. maries of saidtransformers to produce substantially a two-phase relation between their secondary voltages, means for L. connecting `the secondaries of said transformers, switching means andsuitable conductors whereby the ends of said L may be connected in series circuit combination with the electrodes of saidsin le phase furnace, or whereby theends an junction of said i.. may be connected to the electrodes of a two-phase furnace.

9. The method of supplying single phase electric energy to an electric furnace which consists of combining the several phases of a polyphase source of alternating current and a plurality of transformers by connecting the same to said source and to said fur- -nace so as to provide aA quadrature phase v relation between two electric pressures that `combi-ne to produce a resultant electric presile' rature time phase relation between'two electrical pressures which combine to form a,

resultant 'pressure to force single phase current through said are.kv

l1. The method of operatingsingle hase electric furnaces Which consists in sta ilizing the are by means/0f combining the imipedaneee of a plurality of transformers whose secondaries are in series circuit combmatlon with said aic, and Whose primaries are energized jointly b the several phases' ROBERT L. R0Cmvnmz.,v 

